function imp=rcs2imp(rcs,znot,alg)
% imp=rcs2imp(rcs,znot)
%
% RCS2IMP takes a reflectivity vector specified in time and computes
% a corresponding impedence by integrating and exponentiating it. The
% underlying relation is the approximation that 
%  rcs ~ .5 d(log(imp))=> imp=znot*exp(2*Integral(rcs))
%
% rcs ... input column vector of reflection coefficients
% znot ... scalar value of first impedence
% imp ... the resulting impedance
%
% G.F. Margrave
%
% NOTE: This SOFTWARE may be used by any individual or corporation for any purpose
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% By using this software, you are agreeing to the terms detailed in this software's
% Matlab source file.

% BEGIN TERMS OF USE LICENSE
%
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if(nargin<3)
    alg=1;
end
 %integrate the rcs
 if(alg>1)
     ircs=zeros(size(rcs));
     %generate vector of the average of adjacent points in rcs
     n=length(rcs);
     rcs2= (rcs(2:n)+rcs(1:n-1))/2.;
     ircs(2:n)=cumsum(rcs2);
 else
     ircs=cumsum(rcs);%simpler than above
 end
 %exponentiate
 imp=znot*exp(2*ircs);